Sound recording



Sept. 14, 1937.

W. E. BEATTY SOUND RECORDING Filed July 24, 1935 2 Sheets-Shqet l I 4 AMPLIFIEP PECT/F/El? Q 0 0 W 37 4% PIES a 44 20 25 FIEA.

i INVENTOR.

WILLIAM E. BEATTY ATTORNEY Sept. 14, 1937. E, BEATTY 2,093,000

SOUND RECORDING Filed July 24, 1935 2 Sheets-Sheet 2 v 5PEECH Q 4MPLIFIEI?4.

AMPLIFIER PEcT/F/EI? .SPEECH AMPLIFIED INVENTOR. WILLIAM E BEATTY ATTORNE Patented Sept. 14, 1937 PATENT OFFICE SOUND RECORDING William E. Beatty, Hollywood, Calif., assignor to United Research Corporation, Long Island City, N. Y., a corporation of Delaware Application July 24, 1935, Serial No. 32,855

11 Claims.

This invention relates to photographic sound recording apparatus and particularly to apparatus for reducingground noise caused by the transparent portion of the sound track.

As is well known, most of the ground noise head when a sound record of either variable area or variable density type is reproduced is the result of light passing through the apparently clear or transparent portion of the sound track which 1;; contains scratches, particles of dust, enlarged grain, etc. What is desired, therefore, is that the sound track portions be opaque to light at the periods of no sound and only that portion thereof be transparent which is occupied by the modulations.

In the art of variable area recording, it is customary to define a constant intensity beam ,of light by an aperture of a particular shape having at least one straight edge, and then to vary by a moving mirror or similar means the position of the beam across a rectangular slit in accordance with sound waves. The slit is imaged upon the sound track portion of a moving film, the varying widths of opaque portions varying with .the amplitude of the sound waves. Ordinarily at times of no signal half of the light slit is illuminated thus forming equal width. longitudinal strips of opaque and transparent regions constituting the sound track portion, the transparent regions thereof introducing the noise. Although the proportion of opaque to transparent regions is substantially maintained at all volume levels, the noise produced at periods of low levels or at times of no sound is so large that it is detrimental to high quality reproduction.

Heretofore sound recording systems of the variable area type have been equipped to reduce the ground noise by reducing the transparent portion of the track at low volume levels and eliminating it entirely at times'of no sound. This has been accomplished by employing a shutter or shutters which obscure the light up to the boundary of the sound record or by means for biasing the mirrorto vary the center line of the modulations.

When biasing of the oscillating mirror is employecL't'he zero or center of modulation is generally moved as close as possible to one edge of the transparent portion of the film so that all the peaks of both the high and low volume level sounds are as close as possible to the edge of the sound track. Due to the shrinkage of the film or inaccuracies in the film guiding mechanism of the reproducing'apparatus, the film has a tendency-to weave sideways when passing the point of sound translation; this weave being sufficient attimes to allow one end of the light slit to cut off some of the wave peaks. Although the peaks of the high level sounds may be cut off a substantial amount without any apparent distortion of the reproduced sound, this is not true of the low level peaks.

One object of the present invention is to reduce ground noise in the record while keeping the zero line of modulation always in the center of the sound track, and without using either the shutter or biasing arrangement above described.

This is accomplished by moving the light slit itself along a line substantially parallel to its length and in accordance with the volume of sound being recorded. The slit itself allows only the necessary portion of the sound track to receive light, or in other words, produces a slit effective for the particular volume level being recorded.

More particularly describing the invention, reference may be had to the accompanying drawings wherein Fig. 1 is a diagrammatic circuit and opticalarrangement for recording a variable'area noiseless reduction type of sound track.

Fig. 2 is a sectional view ,of a preferred form of slit mechanism and is taken along the line 22 of Fig. 3. s

Fig. 3 is a transverse sectional view taken along the line 3- 3 of Fig. 2 with parts broken away.

Fig. 4 isan enlarged fragmentary view of a positive film having a sound track thereon, the negative of which has been produced by the arrangement shown in Fig. 1.

Fig. 5 isan enlarged fragmentary view of the slit member.

Fig. Bis a diagrammatic circuit. and optical arrangement showing a modifiedform of noise reduction circuit.

Fig. '7 is an enlarged fragmentary view of a positive sound track the negative of which has been madeby the circuit shown in Fig. 6; and

Fig. 8 is adiagrammatic View of a modified form of slit device. 1

Referring to Fig. '1, sound waves directed into the microphone I. are recorded-upon a moving light sensitive film 2. In circuit with the microphone I is a speech amplifier 3 and transformer 4. A galvanometer 5 having an oscillating mir- 0 ror 6 is connected across the secondary of 'the transformer .4. A constant intensity lamp l'projects a beam of light onto the mirror 5 through a condenser lens 8; a second lens 9, and a'mask It]. An edge II of an aperture in the mask Hi forms a sharply defined edge on the beam of light projected on the mirror, this edge of light serving to form an edge on the sound track which represents the sound waves. The beam of light as it is reflected by the mirror 6 passes through a slit device l2, through a pair of objective lenses I3 and onto the film 2. shunted across the output of the speech amplifier 3 is a noise reduction circuit M which passes a portion of the audio current through an amplifier l5 and rectifier |6 from which it is passed into the slit mechanism |2 as will be hereinafter described. Referring now to Figs. 2 and 3, I will now describe the preferred form of slit mechanism. The hollow pole piece I8 is mounted as by screws. it upon the face of a metallic base plate 20. Pole piece |8 has a rectangular opening therethrough as shown by the dotted lines 2| of Fig. 2. A magnetic frame 22 is mounted upon the plate 20 and has a hollow core 23 therein which forms a pole piece adjacent the pole piece l8. An electromagnetic coil 24 is provided around the core 23 and is fed with direct current so as to produce a constant magnetic flux across the pole piece I8 and the pole piece provided by the core 23. A pair of insulated bridges 25 and 26 is mounted on the base plate 26 at either side of the pole piece iii. A pair of current carrying vibratory ribbons 27 and 28 is laid across the bridges'25 and 26 and is clamped thereto by clamping pieces 29 and 36. The ends of the ribbons 2? and 28 are secured upon winches 3|, 32, 33 and 34 which are adapted to vary the tension upon the ribbons21 and 28. Electric conductors 35 and 36 connect the ends of the ribbons 21 and 28 in parallel across the output of the rectifier i6 (Fig. 1). A slit member 37 is cemented across the ribbons 21 and 28 directly in line with the hollow core 23 and the hollow pole piece l8.

Referring to Fig. 5, the ribbons 21, 28 are 'so adjusted that when little or no current is flowing through both the conductors 2? and 28, the

left hand edge of the slit 39, formed in the slit member 3?, lies closely adjacent the edge 40 of the light beam 4|, the edge 46 being produced by edge H of the aperture in the mask Hi. It will be understoodthat the left edge 43 of the slit 39 is adapted to be moved in accordance with the envelope of the sound waves being recorded, while the edge 46 of the light beam 4| traverses the slit 39 in accordance with the volume and amplitude of the sound being recorded. When sounds of low volume are directed into the microphone (Fig. 1) the oscillations of the galvanometer mirror 6 will be correspondingly small to produce a wave form of relatively small height, as shown at S (Fig. 4). A correspondingly low current will be by-passed through the circuit M where it is rectified and applied across the ends of the ribbons 21 and 28, which are so adjusted that the slit member 3'! lies in the position shown by the full lines of Fig. 5 when noor little current is applied. Adjustment of each of the ribbons 21 and 28 is accomplished through adjusting fingers 44 and 45 mounted on insulated blocks 46 and 41 provided on the upper surface of the base plate 26. The fingers 44 and 45 are. attached by screws 48 at one of the ends thereof and. have adjusting set screws 49 contacting the forward ends thereof whereby each of the ribbons 21 and 28 may be transversely adjusted.

When sounds of high volume are recorded in the microphone I (Fig. 1) an increase in current will be sent through the galvanometer 5 as well as through the amplifier and rectifier combination I5 and i6. Thus the size of the wave forms will be increased as shown at L (Fig. 4) and at the same time the increase in current through the ribbons 21 and 28 will produce a greater interaction between both of the ribbons and the magnetic flux flowing between the hollow core 23 and the pole piece Hi to move the slit member 31 toward the position shown by the dotted lines 56 (Fig. 5). As the edge 43 of the slit 39 moves to the left, the curved boundary 5| of the film 52 (Fig. 4) will correspondingly move to the left as at 53 to accommodate the high level wave representations. This variation of the slit member 31 is directly proportional to the envelope of the sound waves being recorded until the mirror 6 reaches the maximum limit of its excursions at which time the slit member 3'! will be moved into the dotted line position 56 shown in Fig; 5. At this point the distance between the edge 43 (in this position) and the edge 46 of the light'beam 4| (at zero position) will equal onehalf the amplitude of the wave form.

Fig. '7 shows a positive film having a sound envelope line 55, the corresponding line in the negative of which is formed by the movable slit device 56 of Fig. 6. The circuit shown in Fig. 6 is the same as that shown in Fig. l with the exception of the noise reduction portion. Instead of passing the envelope current from the noise reduction rectifier l6 directly to the current carrying ribbons 2'! and 28, the current is passedfirst through an electro-magnet 51. A hinged contact 58 is normally held out of engagement with the magnet 51. A second contact 59 is provided in the ribbon circuit 60. When sound waves above a certain predetermined limit are recorded, the increase of current through the electro-magnet 51 will cause the contact 58 to swing into engagement with the contact 59 thus closing the ribbon circuit 60. A battery 6| or other suitable source of power is provided within the circuit 60 to throw the slit member 31 to the left to allow for higher level sound representations. Thus, the line (Fig. '7 will have two positions, 1. e. 62 for low level sounds and 63 for high level sounds.

Fig. '8 shows a modification in which the slit member 65 is formed adjacent the outer edge of a vibratory reed member 66. Reed 66 is secured to a stationary member as at 61. When sound is directed into the microphone 68, a portion of the audio frequency current thus generated is'directed into the circuit 69 to the galvanometer, not shown. The other portion of the audio current being directed through a noise reduction circuit 10 including a rectifier and amplifier combination II and 12, from whence it is passed through a coil 13 formed on the reed 66. Current sent through the coil I8 will produce a magnetic flux withinv the body of the metallic reed 66. The interaction between the magnetic flux produced by the ,coil 13 and the flux produced by the electro-magnets 14 will cause the reed 66 to move to the left in accordance with the volume of the sound being recorded. Thus, when high level sounds are being recorded, the member 66 will be movedinto the dotted line position 15 to allow maximum excursions of the galvanometer mirror to project a light beam through the slit 65 and onto the film. A pair of stops 11 and 18 is provided-to limit the movement of the reed 66 in either direction. Suitable damping means such as an air vane 19 on the reed 66 may be provided.

It is to be understood that the invention, when operating on the rectified or envelope current for variable area records, may be used in conjunction with any type of light beam modulating device.

What is claimed is:

1. An apparatus for photographically recordingsound on a moving film comprising, in combination, a member having an aperture, means for directing a modulated beam of light through said aperture, means for moving said member transversely of the film in accordance with the volume level of the sound to be recorded, and means for focusing an image of said aperture on the film.

2. An apparatus for photographically recording sound upon a moving light sensitive film comprising, in combination, a member having a rectilinear slit therein, means for directing a modulated beam of light through said slit, means for moving said member in accordance with the volume level of the sound waves to be recorded, and means for focusing an image of said slit on the film.

3. An apparatus for recording anti-ground noise type of sound records comprising, in combination, a member having an aperture therein, means for modulating a light beam across said aperture in accordance with sound waves to be recorded, means for moving said aperture member in accordance with the envelope of said sound waves, and means for focusing an image of said aperture on the film.

4. In a device for recording anti-ground noise type of variable area sound records, the combination of a member having a rectilinear slit therer in, means for directing a beam of light through said slit, means for modulating said beam of light in accordance with sound waves to be recorded, means for moving said member in accordance with the envelope of said sound waves, and means for focusing an image of said slit on the film.

5. In a device according to claim 4 wherein said member is moved subtantially parallel to the length of said slit.

6. An apparatus for recording anti-ground noise type of variable area sound film records which comprises the combination of means providing a beam of light, means for varying the Width of said beam in accordance with the wave form of sound waves to be recorded, a member having a rectilinear slit therein placed in the path of said modulated light beam, means for moving said member substantially parallel to the length of said slit and in accordance with the envelope of said sound waves, and means for focusing said slit on the film.

'7. An apparatus for recording sound on a photographic film comprising a magnet, a vibratile electrical conductor in the field of said magnet, an opaque member secured to said conductor and having a light transmitting portion thereon, means for moving said conductor in accordance with the amplitude of sound to be recorded, means for directing a modulated beam of light on said opaque member, said beam being modulated in accordance with sound being recorded, and means for focusing said light transmitting portion of said member on said film.

8. A vibratile electrical conductor adapted to be moved in accordance with sound waves, said conductor having a rectilinear slit movable therewith, means for moving said slit in accordance with the volume of said sound Waves, a light sensitive surface, and means for focusing said slit on said surface.

9. In a sound recording apparatus, the combination of a frame, a pair of vibratile electrical conductors secured to said frame, means for impressing on said conductors electrical currents corresponding to the amplitude of sound to be recorded, an opaque member secured to said conductors intermediate their ends, said member having a rectilinear light transmitting slit therein, means for modulating the light transmitted by said slit in accordance with said sound, a light sensitive surface, and means for focusing said slit on said surface.

10. In a sound recording apparatus, the com sound upon a light sensitive record which comprises modulating a beam of light in accordance with sound waves, directing said modulated beam of light upon a narrow slit extending across the direction of movement of said record to record said sound waves,-focusing said slit upon said record, and moving said slit parallel to the length thereof during said recording in accordance with the volume of said sound waves, whereby the exposure of the unmodulated portion of the sound track is substantially prevented.

WILLIAM E. BEATTY. 

